Selective detection of mercury (II) ion using nonlinear optical properties of gold nanoparticles

SLAM (CD150) receptor homologous peptides block the peste des petits ruminants virus entry into B95a cells

The fusion of haemagglutinin-neuraminidase (HN) protein of peste des petits ruminant (PPR) virus with signaling lymphocyte activation molecules (SLAM) host cell receptor consequences the virus entry and multiplication inside the host cell. The use of synthetic SLAM homologous peptides (i.e., molecular decoy for HN protein of PPR virus) may check PPR infection at the preliminary stage. Hence, the predicted SLAM homologous peptides using bioinformatics tools were synthesized by solid phase chemistry with standard Merrifield's 9-fluorenylmethoxycarbonyl (Fmoc) chemistry and were purified by reverse phase high performance liquid chromatography. The secondary structures of synthesized peptides were elucidated by circular dichroism spectroscopy. The in vitro interactions of these peptides were studied through indirect Enzyme Linked Immuno Sorbent Assay (ELISA) and visual surface plasmon UV-visible spectroscopy. The SLAM homologous peptides were able to interact with the peste des petits ruminant virus (PPRV) with varying binding efficiency. The interaction of SLAM homologous peptide with the PPR virus was ascertained by the change in the plasmon color from red wine to purple during visual detection and also by bathochromic shift in absorbance spectra under UV-visible spectrophotometry. The cytotoxic and anti-PPRV effect of these peptides were also evaluated in B95a cell line using PPR virus (Sungri/96). The cytotoxic concentration 50 (CC50 ) value of each peptide was greater than 1000 μg mL-1 . The anti-PPRV efficiency of SLAM-22 was relatively high among SLAM homologous peptides, SLAM-22 at 25 μg mL-1 concentration showed a reduction of more than log10 3 virus titer by priming of B95a cell line while the use of SLAM-15 and Muco-17 at the same concentration dropped virus titer from log10 4.8 to log10 2.5 and log10 3.1 respectively. The concentration of SLAM homologous peptide (25 μg mL-1 ) to exert its anti-PPRV effect was much less than its CC50 level (>1000 μg mL-1 ). Therefore, the synthetic SLAM homologous peptides may prove to be better agents to target PPRV.

Stimuli-directed selective detection of Cu2+ and Cr2O72- ions using a pH-responsive chitosan-poly(aminoamide) fluorescent microgel in aqueous media

In this work, the preparation of a pH-responsive fluorescent microgel, (NANO-PAMAM-CHT), is presented for the selective detection of Cu2+ and Cr2O72- ions. The NANO-PAMAM-CHT (nanosized polyaminoamide-chitosan microgel) is synthesized via aza-Michael addition reactions in a controlled and stepwise manner in water, using easily affordable starting materials like 1,4-diaminobutane, N,N'-methylene-bis-acrylamide, NIPAM and chitosan. NANO-PAMAM-CHT shows pH-responsive fluorescent properties, whereas the fluorescence intensity shows a pH-responsive change. Due to the selective fluorescence quenching, the microgel can detect both Cu2+ ions and Cr2O72- ions selectively at ambient pH in aqueous medium. Moreover, it can selectively differentiate between Cu2+ ion and Cr2O72- ions at pH ∼3 in water. The limits of detection for Cu2+ ions and Cr2O72- ions are reported as 16.9 μM and 2.62 μM, respectively (lower than the minimum allowed level in drinking water) at pH ∼7. Mechanistic study further reveals the dynamic quenching phenomenon in the presence of Cu2+ ions and static quenching in the presence of Cr2O72- ions.

Syringe Paper-Based Analytical Device for Thiamazole Detection by Hedysarum Polysaccharides-Mediated Silver Nanoparticles

In this paper, silver nanoparticles (AgNPs) were successfully green-synthesized for the first time using Hedysarum polysaccharide (HPS) as a reducing agent, stabilizer, and modifier (HPS-AgNP). Thiamazole could induce the aggregation of HPS-AgNPs in the residue on a cellulose membrane. A syringe paper-based analytical device was creatively established to ensure the tightness, stability, and good repeatability of the test. The color information remaining on the cellulose membrane was converted into gray values using ImageJ software. Hence, the linear regression curve for thiamazole was established as y = 1 + 0.179x with a detection limit (LOD) of 24.6 nM in the relatively wide range of 0.1~10 μM. This syringe paper-based analytical device was successfully applied to the biological samples.

Capping Gold Nanoparticles to Achieve a Protein-like Surface for Loop-Mediated Isothermal Amplification Acceleration and Ultrasensitive DNA Detection

Loop-mediated isothermal amplification (LAMP) is a popular DNA amplification method. Gold nanoparticles (AuNPs) were reported to enhance the efficiency of LAMP, although the underlying mechanism remained elusive. Since AuNPs strongly adsorb a range of ligands, preadsorbed ligands cannot be easily displaced. In this work, we systematically investigated the effect of surface-modified AuNPs on LAMP by varying the order of mixing of AuNPs with each reagent in the LAMP system (Mg²⁺, template DNA, dNTPs, primers, and polymerase). Mixing the AuNPs with the primers delayed the LAMP based on SYBR green I fluorescence. While other orders of mixing had little effect, all accelerated the reaction. We then tested other common ligands including polymers (polyethylene glycol and polyvinylpyrrolidone), inorganic ions (Br^-), proteins, glutathione (GSH), and DNA (A₁₅) on AuNP-LAMP. The boosted AuNP performance on LAMP was most obvious when the AuNPs formed a protein-like surface. Finally, using GSH-capped AuNPs, a detection limit of around 100 copies/μL^-1 of target DNA was achieved. This work has identified a ligand-capped AuNP strategy to boost LAMP and yielded a higher sensitivity in DNA sensing, which also deepens our understanding of AuNP-assisted LAMP.

Plasmonic Nano Silver: An Efficient Colorimetric Sensor for the Selective Detection of Hg2+ Ions in Real Samples

Environmental pollution caused by heavy metal ions has become a major health problem across the world. In this study, a selective colorimetric sensor based on starch functionalized silver nanoparticles (St-Ag NPs) for rapid detection of Hg2+ in real samples was developed. The environmentally friendly green approach was utilized to synthesize starch functionalized silver nanoparticles (St-AgNPs). A multi-technique approach involving UV-Vis absorption spectroscopy, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM) was used for the characterization of St-Ag NPs. These starch functionalized AgNPs were tested for the detection of heavy metals at 25 °C. The screening process revealed clear changes in the AgNPs color and absorption intensity only in the presence of Hg2+ due to the redox reaction between Ag0 and Hg2+. The color and absorption intensity of nanoparticles remain unchanged in the presence of all the other tested metals ion. The proposed method has strong selectivity and sensitivity to Hg2+ ions, with a detection limit of 1 ppm revealed by UV-visible spectrophotometry. The proposed procedure was found to be successful for the detection of Hg2+ in real samples of tap water.

Monolayer-Protected Gold Nanoparticles Functionalized with Halogen Bonding Capability─An Avenue for Molecular Detection Schemes

The use of functionalized nanoparticles (NPs) and their aggregation in the presence of a targeted analyte is a well-established molecular detection strategy predicated on harnessing specific molecular interactions to the NP periphery. Molecules able to specifically interact with the functionalized NPs alter the unique optical and electrochemical properties of the NPs as a function of interparticle spacing. While many intermolecular interactions have been successfully exploited in this manner in conjunction with aqueous NP systems, the use of non-aqueous NPs in the same capacity is significantly less explored. A fundamental interaction that has not been previously investigated in NP schemes is halogen bonding (XB). XB is an orthogonal, electrostatic interaction between a region of positive electrostatic potential (δ+) on a halogen atom (i.e., XB donor) and a negative (δ-) Lewis base (XB acceptor) molecule. To couple XB with NP systems, ligands featuring a molecular structure that promotes XB interactions need to be identified, optimized, and synthesized for subsequent attachment to NPs. Herein, density functional theory (DFT) and NMR techniques are used to identify a strong XB-donor moiety (-C₆F₄I) and a synthetic scheme for a thiolate ligand featuring that functionality is devised and executed with high purity/yield (78%). Ligand-exchange reactions allow functionalization of non-aqueous alkanethiolate-protected gold NPs or monolayer-protected clusters (MPCs) with the XB-donor ligands. Functionalized MPCs (f-MPCs), within both assembled films and in solution, are shown to engage in XB interactions with target XB-acceptor molecules. Molecular recognition events, including induced aggregation of the f-MPCs, are characterized with UV-vis spectroscopy, cyclic voltammetry, TEM imaging, and diffusion-ordered spectroscopy NMR with limits of detection of 50-100 nM for strong XB acceptors. While fundamental exploration of XB interactions is ongoing, this study represents a step toward utilizing XB within molecular detection schemes, an application with implications for supramolecular chemistry, forensic, and environmental chemical sensing.

A dual-channel colorimetric and fluorescent sensor for the rapid and ultrasensitive detection of kanamycin based on gold nanoparticles-copper nanoclusters

In this work, a dual-channel assay was constructed for the colorimetric and fluorescent detection of kanamycin (KAN) based on gold nanoparticles (Au NPs) and copper nanoclusters (Cu NCs). Initially, the fluorescence of Cu NCs was quenched by 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT)-functionalized Au NPs due to the inner filter effect (IFE). The existence of KAN acted as a molecular bridge to interact with AHMT via hydrogen bonds and induced the aggregation of AHMT-Au NPs, leading to a change in the color of the gold colloidal solution from reddish-violet to blue within 2 min. Moreover, the aggregated AHMT-Au NPs can weaken its IFE toward Cu NCs and result in fluorescence restoration. With the sensor employed here, the concentration of KAN can be quantitatively analyzed through double channels, and a low LOD (limit of detection) of 1.9 nM and 1.2 nM was realized by the colorimetric and fluorescent method, respectively. Benefitting from the short response time, high sensitivity, and good reliability, the established assay offered great opportunities for the on-site monitoring of antibiotics in environmental samples.

Merging office/filter paper-based tools for pre-concentring and detecting heavy metals in drinking water

A novel miniaturized and sustainable platform exploiting two merged paper-based substrates has been applied for the programmable pre-concentration of analytes of interest and electrochemical detection of mercury traces in drinking water using printable sensor strips. This strategy represents a novel versatile possibility in merging humble materials maximizing their impacts on analytical and remediation challenges.

Fabrication, calibration, and preliminary testing of microcantilever-based piezoresistive sensor for BioMEMS applications

In this study, the authors demonstrate the fabrication, calibration, and testing of a piezoresistive microcantilever-based sensor for biomedical microelectromechanical system (BioMEMS) application. To use any sensor in BioMEMS application requires surface modification to capture the targeted biomolecules. The surface alteration comprises self-assembled monolayer (SAM) formation on gold (Au)/chromium (Cr) thin films. So, the Au/Cr coating is essential for most of the BioMEMS applications. The fabricated sensor uses the piezoresistive technique to capture the targeted biomolecules with the SAM/Au/Cr layer on top of the silicon dioxide layer. The stiffness (k) of the cantilever-based biosensor is a crucial design parameter for the low-pressure range and also influence the sensitivity of the microelectromechanical system-based sensor. Based on the calibration data, the average stiffness of the fabricated microcantilever with and without Au/Cr thin film is 141.39 and 70.53 mN/m, respectively, which is well below the maximum preferred range of stiffness for BioMEMS applications. The fabricated sensor is ultra-sensitive and selective towards Hg²⁺ ions in the presence of other heavy metal ions (HMIs) and good enough to achieve a lower limit of detection 0.75 ng/ml (3.73 pM/ml).

Limitations for colorimetric aggregation assay of metal ions and ways of their overcoming

The development of analytical methods for the determination of metal ions in water is one of the priority tasks for efficient environmental monitoring. The use of modified gold nanoparticles and the colorimetric detection of their aggregation initiated by ions binding with specific receptors on the nanoparticle surface has high potential for simple testing. However, the limits of this approach and the parameters determining the assay sensitivity are not clear, and the possibilities of different assay formats are estimated only empirically. We have proposed a mathematical description of the aggregation processes in the assay and have estimated the detection limits of an aptamer-based assay of Pb2+ ions theoretically and experimentally. In the studied assay, gold nanoparticles modified with G,T-enriched aptamer were used, and their aggregation caused by the interaction with Pb2+ ions was controlled via a color change. The experimentally determined limit of Pb2+ detection was 700 ppb, which was in good agreement with theoretical calculations. An examination of the model showed that the limiting parameter of the assay is the binding constant of the aptamer-Pb2+ ion interaction. To overcome this limitation without searching for alternate receptors, two methods have been proposed, namely additional aggregation-causing components or centrifugation. These approaches lowered the detection limit to 150 ppb and even to 0.4 ppb. The second value accords with regulatory demands for the permissible levels of water source contamination, and the corresponding approach has significant competitive potential due to its rapidity, simple implementation, and the visual assessment of the assay results.

Fluorescence resonance energy transfer between carbon quantum dots and silver nanoparticles: Application to mercuric ion sensing

Fluorescence resonance energy transfer (FRET) process as a practical and competitive sensing strategy was utilized between carbon quantum dots (C-dots) and silver nanoparticles (Ag NPs) for the determination of mercuric ions. The novel synthesized C-dots with the quantum yield of 84% acted as the donor and Ag NPs operated as the acceptor in the FRET process leading to the fluorescence quenching of the C-dots. In the presence of Hg(II) ions, the FRET-quenched fluorescence emission of the C-dots-Ag NPs system was recovered owing to oxidation of Ag NPs by Hg(II) ions, so that the turn-on fluorescence intensity was directly proportional to the Hg(II) ion concentration. Accordingly, combination of the FRET system with the redox reaction was firstly utilized to construct an innovative turn-off/on fluorescent sensor for the quantification of Hg(II) ion. The calibration plot was linear in the concentration range 0.5-500.0 nmol L^-1 with a determination coefficient (R²) of 0.9965. The limit of detection and limit of quantification were 0.10 and 0.35 nmol L^-1, respectively, according to the IUPAC definition. The method was applied for the determination of Hg(II) ion in lake water, wastewater and tea samples, and the proper relative recoveries (98.0-104.0%) were obtained for the spiked samples. The method has high potential to diagnose trace values of mercuric ions in real samples with high sensitivity and repeatability.

Selective determination of Ag+ in the presence of Cd2+, Hg2+ and Cu2+ based on their different interactions with gold nanoclusters

In this work, a fluorescence method was developed for selective detection of Ag⁺ in the presence of Cd²⁺, Hg²⁺, and Cu²⁺ based on gold nanoclusters (AuNCs). That is, bovine serum albumin (BSA) templated AuNCs with double emission peaks were synthesized using BSA as a protective agent. AuNCs with uniform distribution and average size between 2.0 and 2.2 nm were synthesized using a green and simple method, and showed bright orange-red fluorescence under ultraviolet light. AuNCs have two emission peaks at 450 nm and 630 nm with an excitation wavelength of 365 nm. Under alkaline conditions, Cd²⁺ can combine with the surface sulfhydryl groups of BSA–AuNCs to form Cd–S bonds, which cause AuNCs to aggregate, resulting in an increase in fluorescence intensity at 630 nm. Conversely, due to the d¹⁰–d¹⁰ metal affinity interaction, the addition of Hg²⁺ can reduce the fluorescence peak at 630 nm. Ag⁺ was reduced to Ag⁰ by gold nuclei in AuNCs, forming a stable hybrid Au@ AgNCs species with blue-shifted and enhanced fluorescence. Finally, the paramagnetic behavior of Cu²⁺ combined with BSA causes the excited electrons of the gold cluster to lose their energy via ISC, eventually leading to simultaneous quenching of the two emission peaks. The results show that the limit of detection (LOD) of Ag⁺, Hg²⁺, Cd²⁺ and Cu²⁺ is 1.19 μM, 3.39 μM, 1.83 μM and 5.95 μM, respectively.

A fluorescence method was developed for selective detection of Ag⁺ in the presence of Cd²⁺, Hg²⁺, and Cu²⁺ based on gold nanoclusters. The limit of detection for Ag⁺, Hg²⁺, Cd²⁺ and Cu²⁺ is 1.19 μM, 3.39 μM, 1.83 μM and 5.95 μM, respectively.

Highly selective sensor for the detection of Hg2+ ions using homocysteine functionalised quartz crystal microbalance with cross-linked pyridinedicarboxylic acid

This study reports an insightful portable vector network analyser (VNA)-based measurement technique for quick and selective detection of Hg2+ ions in nanomolar (nM) range using homocysteine (HCys)-functionalised quartz-crystal-microbalance (QCM) with cross-linked-pyridinedicarboxylic acid (PDCA). The excessive exposure to mercury can cause damage to many human organs, such as the brain, lungs, stomach, and kidneys, etc. Hence, the authors have proposed a portable experimental platform capable of achieving the detection in 20-30 min with a limit of detection (LOD) 0.1 ppb (0.498 nM) and a better dynamic range (0.498 nM-6.74 mM), which perfectly describes its excellent performance over other reported techniques. The detection time for various laboratory-based techniques is generally 12-24 h. The proposed method used the benefits of thin-film, nanoparticles (NPs), and QCM-based technology to overcome the limitation of NPs-based technique and have LOD of 0.1 ppb (0.1 μg/l) for selective Hg2+ ions detection which is many times less than the World Health Organization limit of 6 μg/l. The main advantage of the proposed QCM-based platform is its portability, excellent repeatability, millilitre sample volume requirement, and easy process flow, which makes it suitable as an early warning system for selective detection of mercury ions without any costly measuring instruments.

Synthesis of Ag@PANI nanocomposites by complexation method and their application as label-free chemo-probe for detection of mercury ions

A novel optical probe consistinsg of Ag@PANI (silver-polyaniline) nanocomposites was developed for detection of mercury ions (Hg2+). The poly-dispersed Ag@PANI nanocomposites were synthesized by complexation reaction method. We studied structural and functional properties of polymer nanocomposites thoroughly. Ag@PANI nanocomposites consist of fibrous morphology with a mean particle size of 31.39 nm. Ag@PANI nanocomposites consist of face-centered cubic crystal structure with an average crystallite size of 19.41 nm. Raman spectroscopy was used in sensitive and selective detection of Hg2+ ions in dynamic range of 0.01–0.1 ppm with limit of detection of 0.019 ppm. Ag@PANI nanocomposite sensor for Hg (II) ions has shown some sublime results in pH range 3–5. Ag@PANI-based sensing probe can be beneficial for Hg2+ ions detection in highly sensitive biological, chemical and environmental analysis. Our sensing probe has shown good reproducibility, and all recorded observations revealed that sensing probe consisting of Ag@PANI nanocomposites is well suited for detection of Hg2+ ions.

A review on nanostructure-based mercury (II) detection and monitoring focusing on aptamer and oligonucleotide biosensors

Heavy metal ion pollution is a severe problem in environmental protection and especially in human health due to their bioaccumulation in organisms. Mercury (II) (Hg²⁺), even at low concentrations, can lead to DNA damage and give permanent harm to the central nervous system by easily passing through biological membranes. Therefore, sensitive detection and monitoring of Hg²⁺ is of particular interest with significant specificity. In this review, aptamer-based strategies in combination with nanostructures as well as several other strategies to solve addressed problems in sensor development for Hg²⁺ are discussed in detail. In particular, the analytical performance of different aptamer and oligonucleotide-based strategies using different signal improvement approaches based on nanoparticles were compared within each strategy and in between. Although quite a number of the suggested methodologies analyzed in this review fulfills the standard requirements, further development is still needed on real sample analysis and analytical performance parameters.

Azide functionalized porphyrin based dendritic polymers for in vivo monitoring of Hg2+ ions in living cells

A porphyrin cored azide functionalised dendritic polymer was developed as a selective sensor for in vivo monitoring of mercuric ions in living (normal and cancer) cells and in an aqueous medium. The developed sensor could sense mercuric ions even at a nanomolar concentration with a limit of detection value of 0.9 nM. This probe can be used to monitor mercuric ions in living cells due to its low cytotoxicity and high cell permeability. The hydrophilic nature of the polymer makes it a promising candidate for sensing mercuric ions in real water samples. Moreover, the reversibility of this sensing strategy helps in constructing a logic gate, which is particularly useful in smart sensor design.

A SERS-based capillary sensor for the detection of mercury ions in environmental water

Mercury ion (Hg²⁺) is one of the most toxic heavy metal ions which will cause permanent damage to the brain and kidneys. So, it is important to develop a sensitive, simple and reliable approach to detect Hg²⁺. In this work, we report a surface-enhanced Raman scatting (SERS) sensor by decorating the inner wall of capillary with 4,4'-dipyridyl (Dpy) functionalized silver nanoparticles (AgNPs). The main advantage of this sensor is that it can collect samples directly by capillary force and carry out on-site analysis by combining portable Raman spectrometer. In the presence of Hg²⁺, the Dpy molecules would be separated from the surface of AgNPs and coordinated with Hg²⁺, resulting in a decrease in the SERS signal. A linear correlation of Raman intensity with Hg²⁺ concentrations from 1 to 100 part-per-billion (ppb) was obtained for quantitative analysis and the limit of detection (LOD) was determined to be 0.1 ppb. The good reproducibility and selectivity of the sensor were also demonstrated. In addition, the sensors were successfully applied to detect Hg²⁺ in real environmental water samples, and the sampling process provided operation convenience compared to conventional methods. These results indicated that these capillary sensors had great potential for Hg²⁺ detection in practical use.

Magnetically separable and recyclable bamboo-like carbon nanotube-based FRET assay for sensitive and selective detection of Hg2

The global occurrence of toxic hazards in aquatic ecosystems has aroused concern about the potential impacts on the ecological environment and human health in recent decades. Mercury(II) ions that originate from widespread sources including the mining industry, fossil fuel consumption, and industrial wastes are now well known as a highly toxic pollutant. Despite various detection methods which have been reported to sense Hg²⁺, it still poses a great challenge for us to develop a new effective sensing platform to replenish current fluorescent detection techniques. Here, we report a novel fluorescent biosensor using bamboo-like magnetic carbon nanotubes (BMCNTs) and FAM-labeled T-rich ssDNA for efficient detection of Hg²⁺ in aqueous solution. The proposed biosensor shows a good response toward Hg²⁺ detection over a linear response range of 0.05~1 μM (R² = 0.98) with a detection limit of 20 nM. It also exhibits the capability to discriminate Hg²⁺ ions with negligible response to other metal ions, such as Ca²⁺, Cd²⁺, Cu²⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺. Interestingly, the BMCNTs could be separated and recycled easily by using an external magnet, which means a much more cost-effective, easy-to-operate, and eco-friendly method for Hg²⁺ ion detection.

Nonlinear Plasmonic Sensing for Label-Free and Selective Detection of Mercury at Picomolar Level

We present the concept of a nonlinear plasmonic sensing approach for rapid, sensitive, and label-free detection of mercury. Nonlinear plasmonic sensing of mercury relies on a systematic combination of nonlinear optics (NLO) with well-known concepts of amalgamation chemistry and plasmonic properties of gold nanorods. Exploiting the extreme sensitivity of the NLO process toward Hg-induced change in the local electric field of plasmonic nanorods, we succeed in improving the limit of detection (LOD) of mercury by 2-3 orders of magnitude as compared to the commonly used linear localized surface plasmon resonance (LSPR) based sensing. Using our method, an LOD of as low as 58 pM (11 ppt) has been achieved with high selectivity. Nonlinear plasmonic sensing aproach is found to work excellently for detecting mercury in real samples like blood plasma.

Development of a Low-Cost UV-Vis Spectrophotometer and Its Application for the Detection of Mercuric Ions Assisted by Chemosensors

Detection of an environmental contaminant requires the use of expensive measurement equipment, which limits the realization of in situ tests because of their high cost, their limited portability, or the extended time duration of the tests. This paper presents in detail the development of a portable low-cost spectrophotometer which, by using a specialized chemosensor, allows detection of mercuric ions (Hg²⁺), providing effective and accurate results. Design specifications for all the stages assembling the spectrophotometer and the elements selected to build them are presented along with the process to synthesize the chemosensor and the tests developed to validate its performance in comparison with a high-precision commercial laboratory spectrophotometer.

A selective thioxothiazolidin-coumarin probe for Hg2+ based on its desulfurization reaction. Exploring its potential for live cell imaging

Sensing the most toxic heavy metal (mercury) has attracted a lot of attention in recent years due to its extreme harmfulness to both human health and the environment. Thus, we reported herein the synthesis, spectroscopic and kinetic characterization, and biological evaluation of a new thioxothiazolidin coumarin derivative (ILA92), which undergoes a desulfurization reaction induced by mercuric ions (Hg²⁺). This process is the origin of a selective sensing of Hg²⁺ ions in aqueous solution by colorimetric and fluorescent methods. Furthermore, the probe showed great potential for imaging Hg²⁺ in living cells.

Novel formation of Au/Ag bimetallic nanoparticles from a mixture of monometallic nanoparticles and their application for the rapid detection of lead in onion samples

Characterization of gold, silver and gold/silver bimetallic nanoparticles for colorimetric detection of lead in onion samples.

Thermodynamic investigation of the interaction between ionic liquid functionalized gold nanoparticles and human serum albumin for selective determination of glutamine

The excellent biocompatible and monodispersed gold nanoparticles (AuNPs) functionalized by amino based ionic liquid (IL) have been synthesized for the demonstration of their interaction with human serum albumin (HSA). Amino based IL stabilizes the surface of AuNPs and provides a colorimetric sensor platform. The size of synthesized IL–AuNPs was identified by use of transmission electron microscopy (TEM) and dynamic light scattering (DLS) techniques. Molecular interaction of functionalized AuNPs with HSA have been investigated using multispectroscopic techniques, such as UV-Vis, fluorescence and Fourier transform infra-red (FT-IR) spectroscopy. The fluorescence and synchronous fluorescent intensity together indicated that IL–AuNPs exhibits a strong ability to quench the intrinsic fluorescence of HSA via a dynamic quenching mechanism. Moreover, the binding constant (K_a), Stern–Volmer quenching constant (K_SV) and different thermodynamic parameters, namely Gibb's free energy (ΔG), enthalpy (ΔH) and entropy (ΔS) have been evaluated at different temperatures. This interactive study focuses on the nature of surface modification of IL–AuNPs via HSA for selective detection of glutamine (Glu) with a lower limit of detection of 0.67 nM in the linear range of 10–100 nM for Glu.

The excellent biocompatible and monodispersed gold nanoparticles (AuNPs) functionalized by amino based ionic liquid (IL) have been synthesized for the demonstration of their interaction with human serum albumin (HSA).

Pt NPs catalyzed chemiluminescence method for Hg2+ detection based on a flow injection system

Establishing a simple and accurate method for Hg²⁺ detection is of great importance for the environment and human health. In this work, platinum nanoparticles (Pt NPs) with different capped agents and morphologies were synthesized. It was found that Pt NPs exhibited peroxidase-like activity that can catalyze the chemiluminescence (CL) of the luminol system without H₂ O₂ . The most intensive CL signals were obtained by using PVP-capped Pt NPs as catalysis. Based on the fact that Hg²⁺ could further enhance the CL intensity in the Pt NPs-luminol CL system, a Pt NPs-catalyzed CL method based on a flow injection system is developed for the sensitive analysis of Hg²⁺ . When the concentration of Hg²⁺ in the system increases, the CL intensity would together increase, thereby achieving sensitive Hg²⁺ detection. The limit of detection (LOD) was calculated to be 8.6 nM. This developed method provides a simple and rapid approach for the sensitive detection of Hg²⁺ and shows great promise for applications in other complex systems.

Progress in rapid optical assays for heavy metal ions based on the use of nanoparticles and receptor molecules

This review (with 230 refs.) covers recent progress in rapid optical assays for heavy metals (primarily lead and mercury as the most relevant) based on the use of nanoparticles and receptor molecules. An introduction surveys the importance, regulatory demands (such as maximum permissible concentrations) and potential and limitations of various existing methods. This is followed by a general discussion on the use of nanoparticles in optical assays of heavy metals (including properties, basic mechanisms of signal generation). The next sections cover methods for the functionalization of nanoparticles with (a) sulfur-containing compounds (used for modification of nanoparticles or added to the reaction medium), (b) nitrogen-containing compounds (such as amino acids, polypeptides, and heterocyclic molecules), and (c) oxygen-containing species (such as hydroxy and carbonyl compounds). This is continued by a specific description of specific assays based on the use of aptamers as receptors, on the use of deoxyribozymes as synthetic reaction catalysts, of G-quadruplex aptamers, of aptamers in logic gate-type of assays of linear (unstructured) aptamers ("hairpins"), and on the use of aptamers in lateral flow assays. A next section covers assays based on the employment of antibodies as receptors (used in the immunoassay development). The properties of various nanoparticles and their applicability in optical assays are also discussed in some detail. Final sections discuss the selectivity of assays, potential interferences by other cations, methods for their elimination, and also matrix effects and approaches for sample pretreatment. A concluding section discusses current challenges and future trends. Analysis based on enzyme inhibition assay is not treated here but enzyme-like action of some receptor molecules such as DNAzymes is discussed. Graphical abstract Schematic presentation of main principles of application of various nanoparticles with receptor molecules (S-, N-, O-containing, heterocyclic compounds, proteins, antibody, aptamers) for heavy metals ions detection. The included methods cover optical assays with description of mechanisms of interactions and signal generation.

Ultrasensitive colorimetric detection of Hg2+ ions based on enhanced catalytic performance of gold amalgam dispersed in channels of rose petals

We herein present a simple, low-cost, and ultrasensitive colorimetric sensing strategy for the detection of mercury ions (Hg²⁺) that takes advantage of the natural pore structure in rose petals to encapsulate gold nanoparticles (AuNPs).

Selective detection and removal of mercury ions by dual-functionalized metal–organic frameworks: design-for-purpose

In this study, through introducing a new functional group into the structure, the performance and efficiency of MOFs as a sensor for heavy metal cations have been improved.

Novel synthesis of a clay supported amorphous aluminum nanocomposite and its application in removal of hexavalent chromium from aqueous solutions

Synthesis and application of bentonite supported amorphous aluminum nanocomposite as promising material for the removal of Cr(vi) from aqueous solutions.

A Label-free Resonance Rayleigh Scattering Sensor for Detection of Thrombin Based on Aptamer Recognizing

The interaction between thrombin binding aptamer (TBA) and thrombin (TB) was studied by resonance Rayleigh scattering (RRS). In neutral medium, TBA is present in a balanced form between a G-quadruplex structure and a random coil structure, and the TBA can be induced by metal ions to form a G-quadruplex structure. Upon addition of thrombin, the G-quadruplex selectively bound to TB, which resulted in enhanced resonance Rayleigh scattering. The scattering intensities increased proportionally with the concentration of TB from 10 to 50 nM. The method had very high sensitivity and good selectivity, and the detection limit (3δ/s) was 1 nM. In this work, the spectral characteristics of RRS, the optimum conditions of the reaction, and influencing factors for the RRS intensities were investigated. Furthermore, the structure of the TBA-TB complex and the sensing mechanism were explored. The TB sensor was applied to a diluted human serum sample with satisfactory results, indicating the potential of this method to be applied to biological samples. A selective and simple RRS sensor for the detection of trace amounts of TB is proposed based on conformational change of TBA.

Sensitivity limits of biosensors used for the detection of metals in drinking water

Even when present in very low concentrations, certain metal ions can have significant health impacts depending on their concentration when present in drinking water. In an effort to detect and identify trace amounts of such metals, environmental monitoring has created a demand for new and improved methods that have ever-increasing sensitivities and selectivity. This paper reviews the sensitivities of over 100 recently published biosensors using various analytical techniques such as fluorescence, voltammetry, inductively coupled plasma techniques, spectrophotometry and visual colorimetric detection that display selectivity for copper, cadmium, lead, mercury and/or aluminium in aqueous solutions.

A novel logic gate based on liquid-crystals responding to the DNA conformational transition

Described herein is a novel liquid crystal (LC)-based DNA logic gate constructed via employing the reorientation of LCs triggered by metal-ion-mediated DNA probe conformational changes.

Biosensors for wastewater monitoring: A review

Water pollution and habitat degradation are the cause of increasing water scarcity and decline in aquatic biodiversity. While the freshwater availability has been declining through past decades, water demand has continued to increase particularly in areas with arid and semi-arid climate. Monitoring of pollutants in wastewater effluents are critical to identifying water pollution area for treatment. Conventional detection methods are not effective in tracing multiple harmful components in wastewater due to their variability along different times and sources. Currently, the development of biosensing instruments attracted significant attention because of their high sensitivity, selectivity, reliability, simplicity, low-cost and real-time response. This paper provides a general overview on reported biosensors, which have been applied for the recognition of important organic chemicals, heavy metals, and microorganisms in dark waters. The significance and successes of nanotechnology in the field of biomolecular detection are also reviewed. The commercially available biosensors and their main challenges in wastewater monitoring are finally discussed.

Smart app-based on-field colorimetric quantification of mercury via analyte-induced enhancement of the photocatalytic activity of TiO2-Au nanospheres

We have devised a unique strategy for highly sensitive, selective, and colorimetric detection of mercury based on analyte-induced enhancement of the photocatalytic activity of TiO₂-Au nanospheres (TiO₂-Au NSs) toward degradation of methylene blue (MB). Through electrostatic interactions, Au nanoparticles are attached to poly-(sodium 4-styreneulfonate)/poly(diallyldimethylammonium chloride) modified TiO₂ nanoparticles, which then form an Au shell on each TiO₂ core through reduction of Au³⁺ with ascorbic acid. Notably, the deposition of Hg species (Hg²⁺/CH₃Hg⁺) onto TiO₂-Au NSs through strong Au-Hg aurophilic interactions speeds up catalytic degradation of MB. The first-order degradation rates of MB by TiO₂-Au NSs and TiO₂-Au-Hg NSs are 1.4 × 10^-2 min^-1 and 2.1 × 10^-2 min^-1, respectively. Using a commercial absorption spectrometer, the TiO₂-Au NSs/MB approach provides linearity (R² = 0.98) for Hg²⁺ over a concentration range of 10.0 to 100.0 nM, with a limit of detection (LOD) of 1.5 nM. On the other hand, using a low-cost smartphone app that records the color changes (ΔRGB) of MB solution based on the red-blue-green (RGB) component values, the TiO₂-Au NSs/MB approach provides an LOD of 2.0 nM for Hg²⁺ and 5.0 nM for CH₃Hg⁺, respectively. Furthermore, the smartphone app sensing system has been validated for the analyses of various samples, including tap water, lake water, soil, and Dorm II, showing its great potential for on-line analysis of environmental and biological samples. Graphical Abstract ᅟ.